Top Aide in Review of Russia Inquiry Resigns From Justice Dept.

“The idea is you don’t go after candidates, you don’t indict candidates, or perhaps someone that’s officially close to a candidate — that is essentially the same — within a certain number of days before an election,” Mr. Barr said in an April interview with the conservative radio host Hugh Hewitt. “But, you know, as I say, I don’t think any of the people whose actions are under review by Durham fall into that category.”

Mr. Barr assigned Mr. Durham last year to scrutinize the early stages of the Trump-Russia investigation shortly after the special counsel, Robert S. Mueller III, turned in his report that documented Russia’s extensive operations to sabotage the 2016 election and Mr. Trump’s efforts to thwart the inquiry.

Mr. Durham had a history of being assigned to lead sensitive investigations of government conduct, including the F.B.I.’s ties to a crime boss in Boston and the C.I.A. torture of detainees. While he is a longtime career prosecutor, Mr. Trump gave him a political appointment as the U.S. attorney for Connecticut in 2018.

Ms. Dannehy, who successfully prosecuted the former Connecticut governor John G. Rowland on corruption charges, had worked closely with Mr. Durham for years. Her husband, Leonard C. Boyle, is also a close colleague of Mr. Durham’s, serving as the first assistant U.S. attorney in Connecticut. He had previously served as the head of the Terrorist Screening Center, appointed by Mr. Mueller when he was F.B.I. director.

After Mr. Barr assigned Mr. Durham to investigate the Russia inquiry, he asked Ms. Dannehy to return from the private sector to serve as essentially his top investigator on the case. She has played a leading role in questioning witnesses about investigative actions, according to people familiar with the sessions.

This was not the first time that Ms. Dannehy had taken on a high-profile, politically fraught investigation. After a scandal over the George W. Bush administration’s firing of U.S. attorneys who were balking at demands, including by the White House, to bring or speed up voter-fraud cases against Democrats ahead of an election, Attorney General Michael B. Mukasey appointed her to scrutinize whether any laws were broken in one such instance.

While Ms. Dannehy did not find criminal wrongdoing in that dismissal, she suggested in her report that political pressure to rush out a case or charging decision before an election was wrong and potentially constituted obstruction of justice.